This circuit with TTL compatible output was found in a 1968 US documentation. The circuit is powered by 5 V and the frequency can be changed by changing the crystal.
This circuit was found in Sgnetics documentation from the 80's. The circuit also has loudness...
Originally this circuit is from an English magazine, but I found it in Argentina's Radio Chassis...
When the power is cut off, this circuit keeps the flashlight on for a while, allowing it to be...